High-speed microwave modulator



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JOHN F. ZALESKI ATTORNEY 1951 J. F. ZALESKI 2,994,841

HIGH-SPEED MICROWAVE MODULATOR Filed May 28, 1959 2 Sheets-Sheet 2 I I. m F MODULATION D.Cv TERMINATING GENERATOR GENERATOR NETWORK IIIIIIII 46 III! III]; V/////// \\\\\\\\\\\\\\\\\\\\\\\V7/////A u. SI -NLS m an )//////;\\\\\\\\\\\\\\\\\\\\\\\Y W YIIIIIIIIIIIIIIIIIA INVENTOR.

JOHN F. ZALESKI AVITORNEY United States Patent i 2,994,841 HIGH-SPEED MICROWAVE MODULATOR John F. Zaleski, Pleasantville, N.Y., assignor to General Precision, Inc., a corporation of Delaware Filed May 28, 1959, Ser. No. 816,571 12 Claims. (Cl. 332-51) This invention relates to microwave modulators and particularly to devices for modulating microwave energy at frequencies extending into the microwave range.

The purpose of this invention is to provide a microwave modulator which is effective with modulation of any wave form and having any frequency range from direct current up to and including parts of the microwave region.

In one embodiment for modulating frequencies lower than in the microwave region, a tube of ferrite material is positioned in the longitudinal axis of a rectangular or round waveguide. One or more magnetic field sources positioned near the ferrite tube generate a constant field at the ferrite tube. An electrically conducting tube is positioned in the bore of the ferrite tube with its two ends joined to two other conductive tubes which support the central structure and are so positioned transversely in the waveguide that they are at right angles to the electric field of the microwave energy passing though the wave guide. The two ends of each transverse tube are brought out through the waveguide walls, the openings being insulated and protected by microwave chokes. This tube structure is employed to introduce the modulating current into the device. An insulated wire is threaded through the tube for direct-current excitation of a circumferential magnetic field in the ferrite tube.

A second embodiment for higher modulating frequencies omits the chokes and employs resonant stub tuners as mode converters for elficient transmission of the microwave modulation through the bore of the ferrite tube.

In both embodiments the ferrite tube may be composed of any selected ferrite material such as, for example, ferramic R-l, made by General Ceramics Corp., Keasbey, N]. This material contains iron, manganese and magnesium oxides in the molecular proportions of 22Fe O 8MnO and 70MgO.

The operation of the switch is greatly improved by applying a conductive wire helix, a series of metal bands, or a dielectric cylinder to the outside surface of the ferrite tube. The waveguide is preferably hollow, and may be either round or rectangular in form, preferably the latter, or may be an extension of a coaxial line. Any discontinuities that are offered by the supporting tubes and by the ends of the ferrite tube can be matched out by two adjustable susceptances in the waveguide, one in front of the ferrite tube and the other behind it.

A further understanding of this invention may be secured from the detailed description and associated drawings, in which:

FIGURE 1 is a schematic drawing of one form of the invention for modulation at lower than microwave frequencies.

FIGURES 2, 3 and 4 depict three forms which the ferrite component of FIG. 1 may take.

FIGURE 5 is a schematic drawing of another form of the invention for modulation of a microwave carrier at microwave modulation frequencies.

Referring now to FIG. 1, a rectangular waveguide 11 is depicted in section through its longitudinal axis and through the center lines of its narrow sides. A ferrite tube 12 is positioned in the waveguide axis. This tube bears a wire helix 13 wound on its outer surface, the two ends of the helix being left unconnected. A brass tube 14 is centered in the ferrite tube bore by means. of two insulating plugs 16 and 17. The tube 14 is electrically and mechanically secured to two supporting tubes 18 and 19 so that the whole forms an H-sha'ped structure. Both ends of both supporting tubes pass out of the rectangular waveguide 11 through holes centrally positioned in the two narrow sides of the waveguide. Each one of the four exits is provided with a conventional microwave choke structure, illustrated in cross section at 21 and 22 and in plan view at 24 and 26. The choke structure provides rigid support for the tube, as at insulating collar 23. tinuity of the waveguide wall interior surface for microwave energy passing through waveguide 11, and prevents escape of this energy through the tube exit.

An insulated conductive wire 27 is threaded through one end, 18', of the supporting tube 18, through the brass central tube 14, and through one end, 19', of the supporting tube 19. A choke 28 and bypass capacitor 29 protect the direct current circuit from alternating currents which might be induced in it. A direct current generator 31 is connected to supply the two ends of the wire 27. The output of a 30 m.c.p.s. modulation generator, 32, is connected through a transformer coil 33 and a series tuning capacitor 34 between the tube ends 18' and 19'. A bar permanent magnet 36 is positioned parallel to the ferrite tube 12 outside of waveguide 11.

FIG. 2 constitutes a side view of the ferrite tube 12,

FIG. 1. The ferrite tube is made of ferramic R-1 and is 1 /2 inches long, one-quarter inch in diameter, and has a bore one-eighth inch in diameter. The ferrite tube 12 is wrapped with an external helix of bare solid copper wire 13, closely fitted directly thereto and in mechanical and electrical contact therewith. The ends 37 and 38 of this helix are left unconnected. The wire diameterv is 0.020 inch and the helix has 25 turns per inch.

The brass tube 14, FIG. 1, is centered in the bore of the ferrite tube 12 by means of the two insulating plugs 16 and 17, FIGS. 1 and 2, which are drilled to fit the brass tube closely. This is advisable at high modulating frequencies to interpose space between the brass tube and the ferrite tube, thus reducing capacitive losses. The brass tube has an outside diameter of .062 inch and an inside diameter of .040 inch. The Wire threaded through the brass tube consists of insulated stranded copper wire,

size 24 A.W.G. Its diameter over the insulation is 0.037 inch.

FIG. 3 depicts an alternative covering for the ferrite tube of metal bands '39 spaced on the outer surface of the ferrite tube and in mechanical and electrical contact therewith. This figure also depicts permanent magnets 41 and '42 mortised and cemented to the ends of the ferrite tube, the magnets being pierced with bore holes of the same size as the ferrite tube bore. The fields of these magnets supplement or replace the field of the permanent magnet 36, FIG. 1. They are poled so that their fields aid each other.

FIG. 4 depicts another alternative coating for the ferrite tube. This coating is made of a dielectric tube 43 which may, for example, have a dielectric constant of 4. Its internal diameter is 4 inch and fits the ferrite tube closely. Its external diameter is inch. This alternative form, as well as any of the others, may if desired be provided with permanent magnets 44 and 46. In any of these cases the magnet fields may be either in oppo'sition or aiding, the polarity here shown being in opposition.

extreme degradation of. results.

Patented Aug. 1, 1961- It also provides electrical con-.

nal diameter may be varied, but should not be made so large that the ferrite occupies a major part of the volume of the waveguide. The wire helix may be constructed of any conductive wire of any diameter but preferably lying between .030 and .003 inch, tinned or bare, spaced variously between turns. Spacing of the wire from the surfaceof the ferrite degrades the results in proportion to the spacing.

In th operation of the device shown in FIG. 1, microwave energy is applied to one end of the waveguide 11, which transmits the energy to a load connected to its other end. Any impedance discontinuities caused by the ends of the ferrite tube 12 or by the supporting tubes 18 and '19 can be matched out by susceptances, such as tuning screws, in conventional manner. The permanent magnet 36 applies a longitudinal field to the ferrite tube 12 and the direct current from generator '31, flowing through the conductor 27, applies a circumferential field to the ferrite tube 12. By adjusting the strengths and polarities of these two fields combined with the magnetic fields of permanent magnets fixed to the ends of the ferrite tube, if used, a resultant field useful for the present purpose can be obtained. When the tuning susceptances are properly adjusted the insertion loss is small and substantially all microwave energy applied to the waveguide 11 is transmitted through it.

A modulating signal is applied from generator 32. This modulating signal may have any form, such as, for example, that of a sinusoidal pure single frequency, a voice envelope, or a random form having the characteristics of noise. It may alternatively consist of a simplestep voltage change or a train of pulses. The modulation may contain any frequencies which can be carried by the circuit. In'general, the frequency may have any value below microwave frequencies. For microwave modulating frequencies another embodiment, to be described is more suitable. As an explicit example for use in this embodiment the modulation has a center frequency of 30 mc.p.s. The capacitor 34 is adjusted so that it and the inductive winding 33 resonate at 30 mc.p.s., thus greatly enhancing the modulation current. This modulation current is carried through the ferrite tube 12 by the brass tube 14 therein. Since any tube carrying uniform current generates no interior magnetic field, the 30 mc.p.s. modulation is not coupled to the wire 27 within tube 14 or within the members 18' and 19'. Also, the tube 14 interposes no barrier to constant magnetization of the ferrite tube by direct current in the wire 27; The modulating current in tube 14 generates a modulating circumferential magnetic flux in the tube 12, as a result of which the amount of microwave energy transmitted by the waveguide 11 to the load is varied correspondingly, and the modulation products can be detected in the microwave energy at the load.

FIG. depicts an embodiment suitable for use with modulation at microwave frequencies. A rectangular waveguide 47 is adapted to receive carrier microwave energy at one end and, after modulation, deliver it to a load at the other end. A ferrite component 48 is suspended axially in the waveguide 47. This component 48 is depicted as that of FIG. 2 but alternatively may be of any of the other described kinds. The component 48 comprises a ferrite tube 49 through the bore of which runs a metal tube 51. An insulated wire 52 is threaded through the tube 51. So far the embodiment is identical with that described in connection with FIG. 1.

The tube 51 is secured to two supporting tubes 53 and 54 which are brought out through the narrow sides of the rectangular waveguide 47. However, no microwave chokes are employed at the four exits because they would prevent the transmission of microwave frequency modulating energy along these tubes within the eifective bandwidth of the microwave chokes. One end of tube 53 is brought out directly to a modulation generator 56 for generating at microwave frequencies. A metal sleeve 57 surrounds but does not touch the tube 53, is conductively connected to the waveguide at one end and to the modulation generator at the other, and with the tube 53 constitutes a coaxial 2-c0nductor transmission line suitable for carrying modulating energy at microwave frequencies. Similarly, one end of tube 54 is brought out and connected directly to a terminating network 58 suitable for use at the frequency of the modulation generator 56. Tube 54 is surrounded by a sleeve 60, forming with it a coaxial line. The other two ends of the support tubes 53 and 54 are made to serve as tunable stubs by surrounding each with a sleeve, 59 and 61, and by providing each with an adjustable short-circuiting piston, 62 and 63. These pistons are each arranged to short circuit the tube to its sleeve, and are ganged together for common movement by a yoke 64.

It is necessary to apply a continuous magnetic field to the ferrite component 48. This may be done by any of the previously-described means, or by any combination of them. In this embodiment two are indicated, one being the permanent magnet 66 outside of the waveguide and the other being the axial wire 52. This wire is threaded out through the supporting tubes 53 and 54 to a direct-current source 67. The Wire terminals are brought out of the tubes and their surrounding sleeves through small apertures 68, 69, 71, and 72, these being protected by microwave choke structures if desired. Protection against microwave potential is secured by the capacitor 73 connected between the conductor 52 and sleeve 57.

In the operation of this embodiment, microwave carrier energy applied to the waveguide 47 is modulated by microwave modulating energy in the region of the ferrite component 48, and modulation products can be detected and isolated at the load end of the waveguide. The two piston tuning structures are so adjusted in concert as to mode-convert the microwave modulation energy in the coaxial line consisting of tube 53 and sleeve 57 to a mode suitable for transmission through the ferrite component, and to reconvert to the TEM mode for transmission through the coaxial structure 60 to the terminating network 58. 7

These piston tuning structures may alternatively be considered as tuning devices to match out the discontinuities offered by the ferrite structure to microwave energy transmitted from the modulating generator 56 to the terminating network 58. In this aspect these tuning elements are like the tuning screws suggested for use in waveguide 47, and like them reduce or eliminate phase shifts otherwise caused by the discontinuities.

What is claimed is:

1. A modulator comprising, a waveguide section, a territe tube positioned therein and extending longitudinally thereof, an electrically conductive member extending through the bore of said ferrite tube, means for applying a first magnetic field longitudinally to said ferrite tube, means for applying a second magnetic field circumferentially to said ferrite tube, and means applying a modulating signal to said electrically conductive member.

2. A modulator comprising, a waveguide section, a ferrite tube positioned therein and extending longitudinally thereof, an electrically conductive tube extending through the bore of said ferrite tube, an electrically conducting wire extending through the bore of said electrically conducting tube, means applying a constant-amplitude magnetic field to said ferrite tube, means applying direct current to said electrically conducting wire, and means applying a modulating current to said electrically conducting tube.

3. A modulator comprising, a hollow waveguide section, a ferrite tube positioned therein and extending longitudinally thereof, a covering on said tube, said covering having electromagnetic properties differing from those of the space within said waveguide, an electrically conducting tube extending through the bore of said ferrite tube, an electrically conducting wire extending through the bore of said electrically conducting tube, means applying a constant-amplitude magnetic field to said ferrite tube, means applying a direct current to said electrically conducting wire, and means applying a modulating current to said electrically conducting tube.

4. A microwave modulator in accordance with claim 3 in which said covering is a helix of conductive wire wound on the outer surface of said ferrite tube with the two ends of said wire left unconnected.

5. A microwave modulator in accordance with claim 3 in which said covering is a helix of electrically conductive wire wound directly on the outer surface of said ferrite tube with its two ends left unconnected, said wire being composed of metal no larger than 0.04 inch in diameter and said helix having its truns spaced apart.

6. A microwave modulator in accordance with claim 3 in which said covering consists of a plurality of metal rings spaced apart on the outer surface of said ferrite tube.

7. A microwave modulator in accordance with claim 3 in which said covering consists of a cylindrical dielectric sleeve placed directly on the outer surface of said ferrite tube.

8. A microwave modulator comprising, a microwave hollow rectangular waveguide, a cylindrical ferrite tube coaxially positioned therein and extending longitudinally thereof, a covering circumferentially enclosing said ferrite tube, said covering having electromagnetic properties diifering from those of the space within said waveguide, said covering being positioned along the peripheral surface of said ferrite tube and in close contact therewith, an electrically conducting tube extending through the bore of said ferrite tube but spaced from and electrically insulated fi'om the substance thereof, an electrically conducting insulated wire extending through the bore of said electrically conducting tube, means applying a constantamplitude magnetic field to said ferrite tube, means applying a direct current to said electrically conducting insulated wire, and means applying a modulating current to said electrically conducting tube.

9. A microwave modulator in accordance with claim 8 including a pair of straight electrically conducting supporting tubes positioned transversely with said waveguide and extending through the narrow side walls thereof, and means joining the two ends of said electrically conducting tube to respective ones of said electrically conducting supporting tubes.

10. A microwave modulator in accordance with claim 9 in which each of the four ends of said pair of supporting tubes outside of said waveguide is encased in but insulated from a metal tube, each of said supporting tubes and its surrounding metal tube forming a coaxial transmission line.

11. A microwave modulator in accordance with claim 10 in which each end of each of said pair of straight electrically conducting supporting tubes is provided at its exit through said waveguide side wall with a microwave choke and isolating support member.

12. A microwave modulator in accordance with claim 10 in which two adjacent ends of said pair of straight electrically conducting support tuba are each provided with identical short-circuiting pistons for mode transformation, and a yoke connecting said pistons for adjusting them in concert.

References Cited in the file of this patent UNITED STATES PATENTS 2,798,207 Reggia July 2, 1957 2,802,183 Read Aug. 6, 1957 2,849,683 Miller Aug. 26, 1958 2,911,554 Kompfner et al Nov. 3, 1959 OTHER REFERENCES Microwave Modulator Uses Ferrite Gyrator, by Barry et -al., Electronics, May 1955, pp. 139, 140, 141. 

